[Resource Topic] 2016/840: Deja Q All Over Again: Tighter and Broader Reductions of q-Type Assumptions

Welcome to the resource topic for 2016/840

Title:
Deja Q All Over Again: Tighter and Broader Reductions of q-Type Assumptions

Authors: Melissa Chase, Mary Maller, Sarah Meiklejohn

Abstract:

In this paper, we demonstrate that various cryptographic constructions–including ones for broadcast, attribute-based, and hierarchical identity-based encryption–can rely for security on only the static subgroup hiding assumption when instantiated in composite-order bilinear groups, as opposed to the dynamic q-type assumptions on which their security previously was based. This specific goal is accomplished by more generally extending the recent Deja Q framework (Chase and Meiklejohn, Eurocrypt 2014) in two main directions. First, by teasing out common properties of existing reductions, we expand the q-type assumptions that can be covered by the framework; i.e., we demonstrate broader classes of assumptions that can be reduced to subgroup hiding. Second, while the original framework applied only to asymmetric composite-order bilinear groups, we provide a reduction to subgroup hiding that works in symmetric (as well as asymmetric) composite-order groups. As a bonus, our new reduction achieves a tightness of log(q) rather than q.

ePrint: https://eprint.iacr.org/2016/840

Talk: https://www.youtube.com/watch?v=eSPZ5CbKBJg

Slides: https://iacr.org/cryptodb/archive/2016/ASIACRYPT/presentation/27902.pdf

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